The invention is based on a method as generically defined by the main claim.
In terrestrial signal distribution of television signals, both topographic features and above all varying distances of the receiver from the various stations can create very great differences in field intensity at the reception site. The selectivity and linearity of the receiver input stage are at best always limited, and as a result, when all the theoretically possible TV channels and especially neighboring TV channels are occupied with analog-modulated TV programs, problems can occur because of excessive differences between the levels of the channel in use and the neighboring channel and because of cross modulation and intermodulation. The attempt is made to limit these problems by avoiding occupation of neighboring channels. The neighboring channels that are thus not usable are also called forbidden channels. Because of the area coverage and resultant overlaps among various stations for a certain region, the result of this is that by far not all of the terrestrially possible TV channels can be occupied. The resultant scarcity of frequencies is made even worse by the fact that for two stations that are broadcasting the same program, different frequencies have to be provided in the overlapping region, because otherwise common channel interference such as ghost images as a rule occur, because of differences in transit time and extinction zones from interference.
The method according to the invention having the characteristics of the main claim has the advantage over the prior art that the unused forbidden channels can be occupied by digital signals, and in particular digital radio and/or TV broadcasting signals, without causing significant intermodulation and cross modulation with other digital signals or with the analog signals of already-occupied channels. In this way, markedly more channels can be used for terrestrial signal distribution.
Advantageous further features of and improvements to the method disclosed in the main claim are possible by the provisions recited in the dependent claims.
To reduce intermodulation and cross modulation, a modulation of the digital signals by the OFDM method of claim 2 is advantageously used.
Claims 3 and 4 disclose the advantageous provision that at least one digital signal be transmitted at relatively low levels. As a result, the analog signals, which are more vulnerable to interference than digital signals, are not significantly impaired upon reception despite limited selectivity on the part of the receiver input stage.
Reducing the quantity of data in accordance with claim 5 attains the advantage that as many programs and/or data services as possible can be accommodated in the forbidden channels.
The provision of a protective frequency margin between the frequency range of at least one digital signal and at least one neighboring channel leads to an advantageous increase in protection from interference, given the always-limited selectivity of receiver input stages and decoding.
It is advantageous in accordance with claim 7 to use the same frequency and the same channel for a program or data service in the broadcasting by various stations. In this way, the best possible increase in the number of programs for terrestrial signal distribution within a specified frequency range is possible.
It is advantageous according to claim 8 to protect a plurality of digital data, radio and/or TV broadcasting signals against mutual influence on reception by using a protective frequency margin.